This invention relates generally to the art of forming one-piece, multiple groove pulleys from cup-shaped pulley blanks. There are significant problems in manufacturing concentric one-piece, single groove pullelys, and those problems are compounded in the manufacture of multiple groove pulleys. For example, in a double groove pulley, the grooves are separated by a land or circumferential rib located between the pulley grooves and which is an outwardly directed bulge between those grooves. During the formation of the pulley, that land must be supported by internal tooling within the cup, which serves as a back-up as the pulley grooves are being formed. The tooling must be retracted from the land after the formation of the pulley grooves in order to permit removal of the completed pulley from the pulley-making machine. It has been proposed that such tooling be a removable rubber ring in the case of double groove pulleys formed by segmented, outer pulley groove forming dies (U.S. Pat. No. 3,124,090). Other such tooling may be a segmented and expandable inner die employed in a spinning operation (U.S. Pat. No. 2,892,431).
It has been found that when using an internal segmented die to back the land, the segmented die tends to stick in the groove after the crushing operation, since its retracting garter spring is not sufficiently strong to remove the segmented die from its wedged condition. This necessitates the hammering of the blank to free it from the die. A further disadvantage of segmented internal dies is the fact that many of those dies leave tooling marks on the pulley and provide a land which is not truly concentric.
As was stated above, the other type of internal tooling for forming the land between adjacent pulley grooves is a rubber block that will tend to expand into the land upon the application of axial pressure to the cup and which will return to a contracted position when the pressure is no longer applied. Although such rubber blocks do not tend to score the cup, they require frequent replacement and tend to change their dimensions upon repeated machine cyclings.
An acceptable solution to the problem of supporting the land during a groove forming operation is found in U.S. Pat. No. 3,953,995. In that patent there are provided techniques for forming a bulge in the sidewall of a cup-shaped blank while crushing the blank between axially closing dies. As the blank is being crushed, at least two rolls are translated radially into contact with the outer surface of the blank sidewall while the blank is being rotated to form at least two annular pulley grooves in the sidewall of the blank. During the translation, a forming roll is positioned within the blank and is radially shifted away from the longitudinal axis of the cup and into contact with the inner sidewall to form a land between pulley groove pairs.
In substantially all operations involving the formation of grooves in single or multiple groove pulleys, a roughing roll is provided to initially form a groove or grooves in the pulley sidewall and then in a second operation a finish roll or rolls are employed to form the finished groove. Such a two-stage operation is necessary since the finish roll or rolls have relatively sharp peripheries which would tend to thin, or even part, the metal if a drastic one-stage groove-forming operation were employed.
Therefore, the foregoing technique was broken down into a two-stage operation, wherein a rough rolling operation was performed at one station and a finish rolling operation was performed at another station. This situation necessarily lengthens the production cycle time and increases the unit cost of the pulley, which is a low profit margin item. The cycle time to produce single groove pulleys has been drastically shortened by the arrangement shown in U.S. Pat. No. 3,831,414. In that patent, a rough roll is moved slightly in advance of the finish roll to deform the sidewall of the blank in a working operation and partially form the pulley groove while the second forming roll is disposed within the partially formed groove in an idling operation. At the completion of its working operation, the rough roll is disengaged from the partially formed pulley groove and the finish roll is substantially simultaneously moved into a working operation with a negligible amount of nonworking, radial travel. The finish roll is then continuously advanced to an imaginary circle having a diameter equal to the desired root diameter of the pulley groove to cooperate with axially movable die members at their final apposition to completely define the cross section of the pulley being formed. Of course, a single groove operation is not as complex as a double groove forming operation, since there is no necessity for an inner forming member, such as a roller or a segmented die.